Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C263/00—Preparation of derivatives of isocyanic acid
  • C07C263/10—Preparation of derivatives of isocyanic acid by reaction of amines with carbonyl halides, e.g. with phosgene
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C255/00—Carboxylic acid nitriles
  • C07C255/49—Carboxylic acid nitriles having cyano groups bound to carbon atoms of six-membered aromatic rings of a carbon skeleton
  • C07C255/50—Carboxylic acid nitriles having cyano groups bound to carbon atoms of six-membered aromatic rings of a carbon skeleton to carbon atoms of non-condensed six-membered aromatic rings
• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
  • C07C263/00—Preparation of derivatives of isocyanic acid
  • C07C263/18—Separation; Purification; Stabilisation; Use of additives
  • C07C263/20—Separation; Purification

Definitions

• the invention relates to a process for the continuous preparation of isocyanates by reaction of the corresponding amines with phosgene in a reactor in the gas phase in the presence of at least one inert substance, wherein a phosgene-containing stream and a stream containing the amine and the inert substance are fed to the reactor, and wherein the molar ratio of the inert substance to the amino groups in the stream is not subject to wide variations.
• Isocyanates are prepared in large amounts and serve chiefly as starting substances for the preparation of polyurethanes. They are usually prepared by reaction of the corresponding amines with phosgene.
• One possibility of the preparation of isocyanates is the reaction of the amines with the phosgene in the gas phase.
• This process procedure which is conventionally called gas phase phosgenation, is distinguished in that the reaction conditions are chosen such that at least the reaction components amine, isocyanate and phosgene, but preferably all the educts, auxiliary substances, products and reaction intermediate products, are gaseous under the conditions chosen.
• gas phase phosgenation are, inter alia, a reduced phosgene hold-up, the avoidance of intermediate products which are difficult to phosgenate and increased reaction yields.
• the present invention relates exclusively to gas phase phosgenation.
• EP-A-289 840 describes the preparation of diisocyanates by gas phase phosgenation, wherein the preparation takes place in a turbulent flow at temperatures of between 200° C. and 600° C. in a cylindrical space without moving parts. According to the teaching of EP-A-289 840, for it to be possible to carry out the process disclosed in EP-A-289 840 it is essential for the dimensions of the tube reactor and the flow rates in the reaction space to be such that a turbulent flow which, according to the teaching of EP-A-289 840, is characterized by a Reynolds number of at least 2,500 prevails in the reaction space.
• inert gases preferably nitrogen
• vapours of inert solvents such as chlorobenzene, dichlorobenzene, xylene, chloronaphthalene or decahydronaphthalene
• diluents such as chlorobenzene, dichlorobenzene, xylene, chloronaphthalene or decahydronaphthalene
• the specification states that a dilution can be effected adhering to a volume ratio of diamine vapour to inert gas or solvent vapour of from 1:0.5 to 1:2. Nevertheless, the specification expressly denies that the amount of diluents employed could play a critical role (p. 3, column 3,1. 46-48).
• EP-A-570 799 relates to a process for the preparation of aromatic diisocyanates, characterized in that the reaction of the associated diamine with the phosgene is carried out in a tube reactor above the boiling temperature of the diamine within an average contact time of from 0.5 to 5 seconds, As described in the specification, both reaction times which are too long and those which are too short lead to an undesirable formation of solids. A process is therefore disclosed in which the average deviation from the average contact time is less than 6%. Adherence to this contact time is achieved by carrying out the reaction in a tubular flow which is characterized either by a Reynolds number of above 4,000 or by a Bodenstein number of above 100.
• EP-A-699 657 describes a process for the preparation of aromatic diisocyanates in the gas phase, characterized in that the reaction of the associated diamine with the phosgene takes place in a reactor comprising two zones, wherein the first zone, which makes up about 20% to 80% of the total reactor volume, is mixed ideally and the second zone, which makes up 80% to 20% of the total reactor volume, can be characterized by a piston flow.
• the second reaction zone is preferably configured as a tube reactor. However, because at least 20% of the reaction volume is back-mixed in an ideal manner, a non-uniform dwell time distribution results, which can lead to an undesirable increased formation.
• WO2007/028715 discloses a process for the preparation of isocyanates by phosgenation of the corresponding amines in the gas phase in a reactor, characterized in that the reactor employed has a mixing device and a reaction space.
• the reaction space includes in the front region the mixing space in which mixing of the gaseous educts phosgene and amine, optionally mixed with an inert medium, predominantly takes place, which as a rule is accompanied by the start of the reaction.
• the mixing space essentially only the reaction and at most to a minor extent the mixing then takes place in the rear part of the reaction space.
• reaction spaces which are rotationally symmetric to the direction of flow and can be broken down in construction terms essentially into up to four longitudinal sections along the longitudinal axis of the reactor in the course of flow are employed, the longitudinal sections differing in the size of the flowed-through cross-sectional area.
• a disadvantage of the process disclosed is the high flow rate of from preferably 10 to 300 m/s, particularly preferably 40 to 230 m/s, very particularly preferably 50 to 200 m/s, in particular more than 150 to 190 m/s and specifically 160 to 180 m/s, with which the gaseous reaction mixture passes through the reaction space.
• EP-A-1 935 876 describes the advantages of an adiabatic reaction procedure, which lie in avoidance of temperature control problems and relatively high space/time yields.
• an inert medium inert gases or vapours of inert solvents
• the application not going into details with respect to the amounts of streams and ratios of amounts to be adhered to.
• the specification teaches that if a minimum dwell time once determined for the complete reaction for the particular system based on the start temperature, adiabatic increase in temperature, molar ratio of the reactants, dilution gas and amine employed is exceeded by less than 20%, preferably by less than 10%, the formation of secondary reaction products can be largely avoided.
• inert substances for dilution of the educts amine and/or phosgene is thus prior art.
• dilution of the amine is general practice.
• suitable inert substances often nitrogen, act as entraining agents and facilitate vaporization of the amine, as a result of which decomposition reactions (for example with splitting off of ammonia) are reduced.
• TDA abbreviation
• the object of the present invention was therefore to provide a process for the gas phase phosgenation of amines which utilizes the advantages of dilution of the amine with inert substances without the problems described above impairing the progress of the operation.
• the object can be achieved by a process for the continuous preparation of isocyanates by reaction of the corresponding amines with phosgene in a reactor in the gas phase in the presence of at least one inert substance, characterized in that a phosgene-containing stream and a stream containing the amine and the inert substance are fed to the reaction, wherein the molar ratio of the inert substance to the amino groups in the stream
• the molar ratio in (i) and in (ii) is calculated with the sum of the moles of the inert substances.
• Primary amines are preferably employed here.
• Primary aromatic amines which can be converted into the gas phase essentially without decomposition are employed.
• Primary aromatic diamines are preferred in particular.
• TDA toluylenediamine
• NDA naphthyldiamine
• MDA 4,4′-methylenediphenyldiamine
• TDA is particularly preferred.
• Primary amines in particular primary diamines, based on aliphatic or cycloaliphatic hydrocarbons having 2 to 18 carbon atoms are furthermore particularly suitable, Very particularly suitable amines are 1,6-diaminohexane, 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane (IPDA) and 4,4′-diaminodicyclohexylamine.
• IPDA 1-amino-3,3,5-trimethyl-5-aminomethylcyclohexane
• IPDA 4,4′-diaminodicyclohexylamine
• An inert substance in the context of the inventions is a substance which is present in the reaction space in gaseous form at the reaction temperature and does not substantially react with the compounds occurring in the course of the reaction. This means that less than 10 mol %, preferably less than 5 mol %, particularly preferably less than 3 mol % and very particularly preferably less than 1 mol % of the inert substance reacts chemically under the reaction conditions.
• An inert substance in the context of the invention exceptionally particularly preferably does not react chemically at all under the reaction conditions.
• Possible inert substances are, for example, on the one hand those substances which are already gaseous at room temperature, that is to say, for example, nitrogen, noble gases such as helium or argon, and other gases such as carbon dioxide or carbon monoxide.
• possible inert substances are also those which are gaseous only at temperatures above room temperature, that is to say, for example, aromatics such as chlorobenzene, chlorotoluene (o-, m-, p-isomers), dichlorobenzene (o-, m-, p-isomers), toluene, xylene (o-, m.-, p-isomers), chloronaphthalene (all isomers) or decahydronaphthalene.
• nitrogen is particularly preferred, because this meets the criteria with respect to chemical inertness extremely well and is considerably cheaper than noble gases here (which would result in effects of a similar order of magnitude and have an even lower chemical reactivity).
• substances which are also used as a solvent in the process are preferred. Chlorobenzene and dichlorobenzene are particularly preferred.
• the inert substances in the context of the present invention can furthermore be characterized according to their whereabouts in the gas phase process.
• Substances which are already gaseous at room temperature such as, for example, nitrogen, noble gases such as helium or argon, and other gases such as carbon dioxide or carbon monoxide, are essentially sluiced out of the process in gaseous form with hydrogen chloride, the gaseous product formed which is coupled with the reaction, and must therefore constantly be freshly fed in.
• Substances which are gaseous only above room temperature are not sluiced out in gaseous form with hydrogen chloride, the gaseous product coupled with the reaction, but remain in the process and can be used again, where appropriate after purification by distillation, as the inert substance for dilution of the amine.
• the hydrogen chloride can be worked up to chlorine, for example, by the Deacon process known from the literature (WO2004 014845), i.e. oxidatively in the presence of a catalyst. If the hydrogen chloride is worked up by the Deacon process to give chlorine, which can be at least partially used again for the preparation of phosgene by reaction of carbon monoxide with chlorine, it may be advantageous, depending on the exact amounts of streams of inert substance, to employ an inert substance which can be condensed, such as dichlorobenzene, since in this case sluicing of nitrogen out of the phosgenation process is dispensed with in the Deacon process.
• an inert substance which can be condensed such as dichlorobenzene
• the gaseous stream of hydrogen chloride from an isocyanate process contains relatively large amounts of nitrogen, as a result the valuable product HCl gas is diluted in the Deacon process, so that the gas load of the apparatuses increases, which leads to higher apparatus costs. Sluicing out of the amounts of nitrogen from a stream of hydrogen chloride in the Deacon process is furthermore associated with a not inconsiderable outlay, and increases operating costs.
• the amount of inert substance already gaseous at room temperature employed is not too high, if a Deacon process is employed for working up the hydrogen chloride formed it may also be advantageous to employ nitrogen or other inert substances which are gaseous at room temperature.
• inert substance is added in an amount such that
• reaction in the gas phase is to be understood here as meaning that the reaction conditions are chosen such that the educts, reaction intermediate products and products and inert substances metered in remain predominantly in the gas phase during passage through the reaction space during the course of the reaction, in particular to the extent of ⁇ 95% by weight, preferably to the extent of ⁇ 98% by weight, particularly preferably ⁇ 99% by weight, very particularly preferably ⁇ 99.8% by weight and specifically to the extent of ⁇ 99.9% by weight, in each case based on the weight of the reaction mixture.
• Intermediate products in this context are, for example, monoamino-monocarbamoyl chlorides, dicarbamoyl chlorides, monoamino-monoisocyanates and monoisocyanato-monocarbamoyl chlorides formed if diamines are employed, and the hydrochlorides of the particular amino compounds.
• reaction space is understood as meaning the space in which the reaction of the educts and intermediate products takes place, and reactor is understood as meaning the technical device which contains the reaction space.
• a reactor here can also contain several reaction spaces.
• the educts and the inert substances metered in are in general fed to the reaction space via at least one mixing device.
• the process according to the invention can in principle be applied to any reaction space and reactor geometry.
• the reactor has, after the reaction space in which, after mixing of the educts, a conversion of the amine groups into the isocyanate groups of 80%, preferably 90%, particularly preferably 99%, very particularly preferably 99.5% is reached, a rotationally symmetric reaction space with a constant and/or widened flowed-through cross-sectional area.
• the process according to the invention can in principle be applied to any procedure.
• the adiabatic procedure described in EP-A-1 935 876 is preferred.
• the process described is also advantageous in an isothermal procedure, since in spite of the isothermal procedure, which can be achieved, for example, by cooling the exothermic reaction externally, because of the speed of the gas phase reaction a very rapid change in the reactor temperature results, which cannot be compensated sufficiently rapidly because of the inertia of the coolant system, so that in the case of an isothermal procedure of the reaction temperature variations also occur in the reactor, with the disadvantages described in the prior art.
• the starting amines are preferably vaporized and are heated to 200° C. to 600° C., preferably 200° C. to 500° C., particularly preferably 250° C. to 450° C., and are fed to the reaction space in a form diluted with at least one inert substance according to the above definition.
• the inert substance is fed to the vaporization, and particularly preferably the inert substance is fed to the vaporization at the point at which the amine is at least completely or partially converted from the liquid into the gaseous phase.
• Inert substances which are already gaseous at room temperature are preferably fed to the vaporization in gaseous form.
• Inert substances which are gaseous only above room temperature can be introduced into the amine vaporization in either liquid form or gaseous form, i.e. after prior vaporization.
• the inert substances which are gaseous only above room temperature first optionally to be mixed with the amine in the desired ratio in a suitable container and for the stream obtained in this way to be vaporized together.
• the inert substance fed in is gaseous at room temperature, it is preferably fed to the vaporization with a temperature of from ⁇ 30° C. to 600° C., preferably 0 to 500° C., particularly preferably 50 to 400° C.
• Various apparatuses are suitable for achieving this temperature, such as, for example, tube bundle heat exchangers with a coolant or heating agent or electrically operated heaters or other apparatuses.
• the inert substance fed in which is gaseous at room temperature particularly preferably has a temperature difference from the boiling point of the amine at the given vaporization pressure of not more than 150° C., preferably not more than 100° C.
• the inert substance fed in is gaseous only above room temperature, if it is fed into the reactor in gaseous form it is first vaporized and preferably fed to the amine vaporization with a temperature of from 200° C. to 600° C., particularly preferably with a temperature of from 250° C. to 500° C.
• the gaseous inert substance fed in which is gaseous only above room temperature particularly preferably has a temperature difference from the boiling point of the amine at the given vaporization pressure of not more than 150° C., preferably not more than 100° C.
• the temperature of the inert substance can vary widely. A temperature range of from minus 30° C. to 200° C., and preferably 0 to 180° C. is possible. It is also possible for the mixture obtained from the amine and the inert substance which is gaseous only above room temperature to be heated together and to be passed into the vaporization as a mixture. However, it is also possible to heat the two streams separately and to combine them only in the vaporization.
• a sufficient constant nature according to the invention of the ratio of the streams is preferably achieved by a constant and uniform, preferably uniform over time, mixing of the streams.
• a sufficient constant nature of the ratio of the streams is achieved by a procedure in which the smaller of the streams in amount, i.e. the inert substance fed in, is fed in with a constant amount and in a stable manner over time.
• Suitable measures by means of which inert compounds which are already gaseous at room temperature can be fed in constantly and in a stable manner over time are known to the person skilled in the art. It may be mentioned here by way of example but not limitation, however, that the gas pressure of the gaseous stream fed in is sufficiently high to render possible a regulated and stable feeding in.
• the pressure in the feed, i.e. in the feed line directly before entry into the vaporizer, of the inert substance fed in is thus preferably higher than the pressure which prevails in the vaporization apparatus.
• the pressure is at least 10 mbar, very particularly preferably at least 50 mbar, and particularly preferably at least 150 mbar higher than the pressure in the vaporization apparatus.
• the pressure is not more than 100 mbar higher.
• inert substances fed into the reactor in gaseous form are measured, and stirred into the reactor in a regulated manner.
• Suitable measuring instruments and regulating instruments are prior art. Other measures are likewise possible.
• the sufficient constant nature of the ratio of the streams is achieved by mixing liquid streams.
• the smaller of the streams in amount, i.e. the inert stream is fed in with a constant amount and in a stable manner over time.
• Suitable measures for metering liquid streams in a constant manner are known to the person skilled in the art. Suitable metering in a constant amount and in a stable manner over time can be effected, for example, with a metering pump, but filling into a container and mixing, for example by means of a stirrer, is also conceivable. Other measures are likewise possible.
• these measures ensure that within a period of 20 minutes the molar stream of inert substance or the sum of the molar streams of all the inert substances changes by not more than 99%, preferably not more than 80%, particularly preferably not more than 60%.
• marked variations in the ratio of the sum of the molar streams of all the inert-substances to the molar stream of the amine groups are avoided, so that within a period of 20 minutes this ratio changes by not more than 99%, preferably not more than 80%, particularly preferably not more than 60%.
• the vaporization of the starting amines can be carried out in all known vaporization apparatuses.
• Vaporization systems in which a small work content is led with a high circulating output over a falling film evaporator, wherein to minimize the exposure of the starting amines to heat the vaporization operation is assisted by feeding in at least one inert substance, are preferably employed.
• vaporization systems in which a small work content is circulated over at least one micro-heat exchanger or micro-evaporator are employed.
• the use of appropriate heat exchangers for vaporization of amines is disclosed e.g. in EP-A-1 754 698.
• the apparatuses disclosed in paragraphs [0007] to [0008] and [0017] to [0039] of EP-A-1 754 689 are preferably employed in the process according to the invention.
• the vaporized mixture of amine and at least one inert substance can also contain contents of non-vaporized droplets of amine, and in the case where those inert substances which are gaseous only above room temperature are used, under certain circumstances also additionally contents of non-vaporized inert substance.
• the vaporized mixture of amine and inert substance can thus be in the form of an aerosol.
• the vaporized mixture of amine and inert substance essentially contains no droplets of non-vaporized amine and/or non-vaporized inert substance, that is to say a maximum of 0.5% by weight, particularly preferably a maximum of 0.05% by weight of the vaporized mixture of amine and inert, substance, based on the total weight of the vaporized mixture of amine and inert substance, is in the form of non-vaporized droplets.
• the remaining part of the vaporized mixture of amine and inert substance is in vaporous form.
• the vaporized mixture of amine and at least one inert substance contains no droplets of non-vaporized contents.
• the mixture of amine and at least one inert substance is brought to the desired use temperature via an after-heater.
• the vaporization and superheating of the starting amines/inert substances furthermore is preferably carried out in several stages in order to avoid non-vaporized droplets in the gas stream of amine and at least one inert substance.
• Multi-stage vaporization and superheating steps in which droplet separators are incorporated between the vaporization and superheating systems and/or the vaporization apparatuses also have the function of a droplet separator are preferred in particular. Suitable droplet separators are described e.g. in “Droplet Separation”, A. Bürkholz, VCH Verlagsgesellschaft, Weinheim—New York—Basle—Cambridge, 1989. Droplet separators which cause a low pressure loss are particularly preferred.
• the vaporized mixture of amine and at least one inert substance is brought to the desired use temperature via at least one after-heater, which also functions as a droplet separator.
• this after-heater has a liquid drain in order to ensure constant emptying of the separator.
• the mixture of amine and at least one inert substance which has been preheated to its intended temperature is fed with an average dwell time of from preferably 0.01 to 60 s, very particularly preferably from 0.01 to 30 s, particularly preferably 0.01 to 15 s to the reactor or the mixing device thereof for reaction.
• the risk of a renewed formation of droplets is counteracted here via technical measures, e.g. an adequate insulation to avoid losses by radiation.
• the reactor running time is increased significantly by generation of an essentially droplet-free gas stream of amine and at least one inert substance before entry into the reactor.
• feeding of the gas stream of amine and at least one inert substance to the reactor or at least one mixing device thereof takes place with a low pressure loss without a regulating device.
• regulated feeding is likewise possible.
• a division of the gas stream of amine and at least one inert substance into several part streams, which are then fed as described e.g. in EP-A-1 449 826 in paragraphs [0019] to [0022] to a reaction space or, as described e.g. in WO 2008/055898 p. 8, 1. 25 to p. 15, 1. 31 and in particular p. 23, 1. 19-31, to several mixing devices, is also possible.
• the feeding of the part streams preferably also takes place with a low pressure loss without additional regulating devices.
• separately regulated feeding of the part streams is also possible.
• phosgene in excess with respect to the amine groups to be reacted.
• a molar ratio of phosgene to amine groups of from 1.1:1 to 20:1, preferably 1.2:1 to 5:1 is present.
• the phosgene is also heated to temperatures of from 200° C., to 600° C. and, optionally likewise diluted with at least one inert substance according to the above definition, is fed to the reaction space.
• regulated feeding of the phosgene stream to the reactor or at least one mixing device thereof takes place.
• feeding with a low pressure loss without a regulating device is likewise possible.
• separately regulated feeding of the phosgene part streams preferably takes place.
• the process according to the invention is preferably carried out such that the separately heated reaction partners are introduced via at least one mixing device into at least one reaction space, mixed, and reacted taking account of suitable reaction times under a preferably adiabatic reaction procedure.
• the isocyanate is then condensed by cooling the gas stream, the cooling taking place down to a temperature above the decomposition temperature of the corresponding carbamic acid chloride, that is to say, for example, toluylenediamine acid chloride in the case of TDA.
• the necessary dwell time for reaction of the amine groups with the phosgene to give isocyanate is between 0.05 and 15 seconds, depending on the nature of the amine employed, the start temperature, where appropriate the adiabatic increase in temperature in the reaction space, the molar ratio of amine employed and phosgene, the nature and amount of the at least one inert substance and the reaction pressure chosen.
• Reactors with essentially rotationally symmetric reaction spaces in which the gaseous educts and at least one inert substance are fed to the at least one mixing space in accordance with the jet mixer principle are particularly preferably employed.
• the substance streams fed in i.e. amine and at least one inert substance on the one hand and phosgene, optionally diluted with inert substances, on the other hand
• the substance streams fed in preferably enter into the at least one mixing space of the reactors with a speed ratio of 2-20, particularly preferably 3-15, very particularly preferably 4-12.
• the mixture of amine and at least one inert substance is fed with the higher flow rate to the at least one mixing space of the reactors.
• neither the reaction space nor any mixing units or mixing spaces have heating surfaces, which could give rise to exposure to heat with the consequence of secondary reactions, such as isocyanurate or carbodiimide formation, or cooling surfaces, which could give rise to condensation with the consequence of deposits.
• the components are preferably reacted adiabatically in this way, apart from any losses by radiation and conduction.
• the adiabatic temperature increase in the mixing unit and reactor or reactor is established solely via the temperatures, compositions and relative meterings of the educt streams and the dwell time in the mixing units and the reactors.
• the gaseous reaction mixture which preferably comprises at least one isocyanate, phosgene, at least one, preferably exactly one, inert substance and hydrogen chloride, is preferably freed from the isocyanate formed.
• This can be carried out, for example, by subjecting the reaction mixture continuously leaving the reaction space to a condensation in an inert solvent, as has already been recommended for other gas phase phosgenations (EP-A-0 749 958).
• the condensation is carried out by a procedure in which the reaction space employed in the process according to the invention has at least one zone into which one or more suitable streams of liquid (“quench liquids”) are sprayed for discontinuation of the reaction of the amines employed and the phosgene to give the corresponding isocyanates.
• quench liquids suitable streams of liquid
• rapid cooling of the gas mixtures can be carried out without the use of cold surfaces.
• the at least one zone is integrated into a quenching stage, such as has been disclosed e.g. in EP-A-1 403 248.
• a quenching stage such as has been disclosed e.g. in EP-A-1 403 248.
• several cooling zones are employed. Integration and operation of these at least two cooling zones are preferably effected with a quenching stage. This is disclosed with respect to construction and operation in EP-A-1 935 875.
• the integrated combination of the at least one cooling zone of a reactor with a quenching stage such as has been disclosed in EP-A-1 935 875
• the corresponding integrated combination of the cooling zones of several reactors with a quenching stage is likewise possible.
• the integrated combination of a reactor with at least one cooling zone with a quenching stage is preferred.
• the throughput capacity of the reactor employed under the reaction conditions required according to the invention is>1 t of amine/h, preferably 2-50 t of amine/h, particularly preferably 2-12 t of amine/h. These values particularly preferably apply to toluylenediamine, 1,6-diaminohexane and to isophoronediamine.
• throughput capacity is to be understood as meaning that the stated throughput capacity of amine per h can be reacted in the reactor.
• the temperature of the at least one cooling zone is preferably chosen such that on the one hand it is above the decomposition temperature of the carbamoyl chloride corresponding to the isocyanate, and on the other hand the isocyanate and inert substances employed which are gaseous only above room temperature to the greatest extent condense or to the greatest extent dissolve in the solvent.
• Excess phosgene, hydrogen chloride and inert substances which are gaseous at room temperature are preferably to the greatest extent not condensed or not dissolved in the condensation or quenching stage.
• Solvents kept at a temperature of from 80 to 200° C., preferably 80 to 180° C., such as, for example, chlorobenzene and/or dichlorobenzene, or isocyanate or mixtures of the isocyanate with chlorobenzene and/or dichlorobenzene kept in this temperature range are particularly suitable for selective isolation of the isocyanate from the gaseous reaction mixture.
• the person skilled in the art can easily predict what weight content of the isocyanate condenses in the quenching or passes through this without being condensed. It is likewise easy to predict what weight content of the excess phosgene, hydrogen chloride and at least one inert substance passes through the quenching without being condensed or dissolves in the quenching liquid.
• the pressure gradient preferably exists between the educt feed lines before the mixing on the one hand and the exit from the condensation or quenching stage on the other hand.
• the absolute pressure in the educt feed lines before the mixing is 200 to 3,000 mbar and after the condensation or quenching stage is 150 to 2,500 mbar.
• the gas mixture leaving the condensation or quenching stage is preferably freed from residual isocyanate in a downstream gas wash with a suitable wash liquid, and is preferably the then freed from excess phosgene in a manner known per se.
• This can he carried out by means of a cold trap, absorption in an inert solvent (e.g. chlorobenzene or dichlorobenzene) or by adsorption and hydrolysis on active charcoal.
• the hydrogen chloride gas passing through the phosgene recovery stage can be recycled in a manner known per se for recovery of the chlorine required for the phosgene synthesis.
• the wash liquid obtained after its use for the gas wash is then preferably at least partially employed as the quench liquid for cooling the gas mixture in the corresponding zone of the reaction space.
• the isocyanates are subsequently preferably prepared in a pure form by working up the solutions or mixtures from the condensation or quenching stage by distillation.
• 20.5 kmol/h of a mixture comprising 2.4- and 2,6-toluylenediamine in the weight ratio of 80% to 20% are vaporized together with 17.85 kmol/h of nitrogen at approx. 280° C. and are passed in gaseous form to a rotationally symmetric tube reactor with a downstream isocyanate condensation stage with a temperature above 300° C.
• this gaseous phosgene is fed to the tube reactor, likewise with a temperature above 300° C.
• the streams are injected into the mixing zone through a nozzle and mixed and enter into the reaction space.
• the reaction in the reaction space takes place adiabatically within a dwell time of less than 10 seconds.
• the gas mixture is passed through a condensation stage and is thereby cooled to a gas temperature of approx. 165° C.
• the condensate obtained is fed to a distillation sequence and gives pure TDI.
• the non-condensed gas mixture is washed with o-dichlorobenzene in a subsequent washing and the by-product HCl is separated from the excess phosgene by absorption.
• the amount of nitrogen first falls to approx. 20% of the original value, in order then to rise to approx. 150% of the original value.
• the amount of TDA first falls to approx. 40% of the original amount, in order then to rise to approx. 125% of the original amount.
• the average dwell time in the reactor varies by more than + ⁇ 10%. Inspection of the mixing nozzle shows deposits. The temperature variations measured on the outer wall on the reactor are + ⁇ 3° C.
• 20.5 kmol/h of a mixture comprising 2.4- and 2,6-toluylenediamine in the weight ratio of 80% to 20% are vaporized together with 17.85 kmol/h of nitrogen at approx. 280° C. and are passed in gaseous form to a rotationally symmetric tube reactor with a downstream isocyanate condensation stage with a temperature above 300° C.
• this gaseous phosgene is fed to the tube reactor, likewise with a temperature above 300° C.
• the streams are injected into the mixing zone through a nozzle and mixed and enter into the reaction space.
• the reaction in the reaction space takes place adiabatically within a dwell time of less than 10 seconds.
• the gas mixture is passed through a condensation stage and is thereby cooled to a gas temperature of approx. 165° C.
• the condensate obtained is fed to a distillation sequence and gives pure TDI.
• the non-condensed gas mixture is washed with o-dichlorobenzene in a subsequent washing and the by-product HCl is separated from the excess phosgene by absorption.
• the amount of nitrogen based on the TDA gas amount changes by not more than plus/minus 5%.
• the average dwell time in the reactor varies by not more than 6%, no temperature changes are measured on the reactor wall. Inspection of the mixing nozzle shows no deposits.

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• 2009
  • 2009-07-09 DE DE102009032414A patent/DE102009032414A1/de not_active Withdrawn
• 2010
  • 2010-06-26 KR KR1020127000445A patent/KR20120038436A/ko not_active Abandoned
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  • 2010-06-26 JP JP2012518791A patent/JP5717735B2/ja not_active Expired - Fee Related
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  • 2010-06-26 CN CN201080031231.9A patent/CN102498092B/zh active Active
  • 2010-06-26 EP EP10729809.3A patent/EP2451774B1/de active Active
  • 2010-06-26 US US13/382,609 patent/US8563767B2/en active Active
  • 2010-07-08 TW TW099122408A patent/TWI457315B/zh not_active IP Right Cessation

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